Why does this invalid-looking code compile successfully on g++ 6.0? [duplicate]
Solution 1:
This looks to be an bug/feature/issue with g++ in all of the versions I can test it on. Running
int main()
{
int(*){} Is it C++14 or any other language?
}
On godbolt.org for all versions of g++ with no compilation flags give the following assembly ouput.
main:
pushq %rbp
movq %rsp, %rbp
movl $0, %eax
leave
ret
The only diagnosis I get is on godbolt.org and that is
!!warning: extended initializer lists only available with -std=c++0x or -std=gnu++0x
Clang, ICC and MSVS all fail to compile this.
EDIT:
From the comments zwol filed a bug with gcc on this. The bug report can be found here.
Solution 2:
I've run the command on my Fedora VM with g++ version 5.1.1 and found the following:
[user:~] 1 $ g++ -fdump-tree-original-raw tmp.cpp
tmp.cpp: In function ‘int main()’:
tmp.cpp:3:11: warning: extended initializer lists only available with -std=c++11 or -std=gnu++11
int(*){} Is it C++14 or any other language?
^
However that still managed to compile... So I've dumped the AST and got this:
$ cat tmp.cpp.003t.original
;; Function int main() (null)
;; enabled by -tree-original
@1 return_expr type: @2 expr: @3
@2 void_type name: @4 algn: 8
@3 init_expr type: @5 op 0: @6 op 1: @7
@4 type_decl name: @8 type: @2 srcp: <built-in>:0
note: artificial
@5 integer_type name: @9 size: @10 algn: 32
prec: 32 sign: signed min : @11
max : @12
@6 result_decl type: @5 scpe: @13 srcp: tmp.cpp:1
note: artificial size: @10
algn: 32
@7 integer_cst type: @5 int: 0
@8 identifier_node strg: void lngt: 4
@9 type_decl name: @14 type: @5 srcp: <built-in>:0
note: artificial
@10 integer_cst type: @15 int: 32
@11 integer_cst type: @5 int: -2147483648
@12 integer_cst type: @5 int: 2147483647
@13 function_decl name: @16 type: @17 scpe: @18
srcp: tmp.cpp:1 lang: C
link: extern
@14 identifier_node strg: int lngt: 3
@15 integer_type name: @19 size: @20 algn: 128
prec: 128 sign: unsigned min : @21
max : @22
@16 identifier_node strg: main lngt: 4
@17 function_type size: @23 algn: 8 retn: @5
prms: @24
@18 translation_unit_decl
@19 identifier_node strg: bitsizetype lngt: 11
@20 integer_cst type: @15 int: 128
@21 integer_cst type: @15 int: 0
@22 integer_cst type: @15 int: -1
@23 integer_cst type: @15 int: 8
@24 tree_list valu: @2
Which is too big to fit inside a comment but should be useful in determining what is going on. I'm still going through this but I'm just posting this information for others to build from.
Which is visualized like this 
.